Five months after West Nile virus made its first Western Slope appearance in Craig, local and state veterinarians say summer months should bring more cases of the mosquito-borne illness.
This, as the same health officials urge horse owners to vaccinate their animals soon.
"We're telling everyone to start with shots in the spring, not when (horses) are going to be at most risk," said Stacey Hudelson, McCandless Animal Hospital veterinarian who responded to the scene of September's virus-stricken horse in a pasture east of the city near the Yampa River.
A second horse brought to the area by a hunting party from Fort Collins was treated at the hospital within weeks of the first incident, Hudelson said.
"All cases in the state occurred late-season so it didn't really have a chance to get going," said John Pape, epidemiologist with the Colorado Department of Public Health and Environment.
The specific mosquito species carrying the virus should return in April or May, while their populations peak late summer, he said.
The vaccination is delivered in two phases -- a process that should be repeated annually around spring, officials said. Three to six weeks after receiving an initial shot, animals should receive a booster. Immunity takes another four weeks.
McCandless offers the vaccine at $18 each.
Some 13 Colorado residents last year tested positive in non-fatal cases of the virus, while 380 cases were confirmed in horses -- 95 of which died, according to state health department.
Five to 10 percent of animals exposed actually develop the illness, leading to death in 30 percent of cases.
Pape said responses vary in humans and horses, but typically appear seven to 10 days after a bite from an infected mosquito. Flu-like symptoms are possible, usually among adults 60 years and older, Pape said.
West Nile virus attacks horses' nervous systems, which is shown by uncoordinated movement and trembling muscles.
Pape said steps taken around residents' homes and property can eliminate breeding grounds for West Nile-carrying mosquitoes. Irrigated fields are the most attractive location for the insects, he said.
"Any place where water pools is a wonderful breeding ground."
Paul Shockley can be reached at 824-7031 or at firstname.lastname@example.org.